Diethylenetriaminepenta (methylene phosphonic) acid (DTPMP) was first used as a dopant to modify hydroxyapatite and applied to remove Pb2+. The adsorption capacity of modified hydroxyapatite for Pb2+ can reach 2185.92 mg/g, which was 10.4 times that of commercial nanohydroxyapatite. The characterizations after adsorption of Pb2+ indicated the existence of chelation and the formation of the low bioavailability Pb10(PO4)6(OH)2. Moreover, the interaction of different components containing DTPMP, HAP, and pollutant Pb2+ was investigated by molecular dynamics (MD) simulation, which indicated that the organic-phosphonic group of DTPMP (PO3H-) had a stronger complex effect with calcium ions or lead ions than that of the inorganic-phosphate group of HAP (PO43-) with the two metal ions, which affected the crystallinity of HAP, and greatly improved the removal effect of DTPMP doped HAP composites for Pb2+ contaminants, the existence of amino groups can further enhance the affinity between DTPMP and HAP or lead ions. The chelation mechanism of DTPMP and Pb2+ was probed in depth by combining basin analysis, topology analysis of atoms in molecules (AIM), electron localization function (ELF) analysis, bond order density (BOD) & natural adaptive orbital (NAdO)analysis and orbital component analysis.
Keywords: Adsorption mechanism; Heavy metal ions; Hydroxyapatite composite; Molecular dynamics (MD) simulation.
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